It has been known that expanded molded articles comprising a polystyrene-based resin have excellent rigidity, thermal insulation properties, lightweight properties, water resistance, and expansion moldability. Therefore, this expanded molded articles have been widely used as cushioning materials and thermal insulation materials for building materials. However, the expanded molded articles comprising a polystyrene-based resin have the problem of inferior chemical resistance and impact resistance.
On the other hand, it has been known that expanded molded articles comprising a polyethylene-based resin have excellent chemical resistance and impact resistance. Therefore, this expanded molded articles are used in vehicle-related components. However, the polyethylene-based resins have inferior retention of a blowing agent, and thus it is necessary to precisely control expansion molding conditions. This leads to the problem of increase in production costs. In addition, this expanded molded articles have the problem of inferior rigidity compared to the expanded molded articles comprising the polystyrene-based resin.
In order to solve such aforementioned problems associated with the expanded molded articles comprising the polystyrene-based resin or polyethylene-based resin, various expanded molded articles obtained from composite resin particles of a polystyrene-based resin and a polyethylene-based resin e been reported. This expanded molded articles have both excellent rigidity and expansion moldability provided by the polystyrene-based resin and excellent chemical resistance and impact resistance provided by the polyethylene-based resin. However, such expanded molded articles have the problem of high dependency of mechanical characteristics on temperature. In order to suppress such temperature dependency, expanded molded articles using high-density polyethylene as a polyethylene-based resin have been reported (Japanese Unexamined Patent Application, First Publication No. 2012-025347),